Cat urinary changes: reading the litter tray and spotting a blocked cat

Quick answer

A male cat straining in the litter tray and producing nothing is one of the few genuine same-hour emergencies in cats. A blocked urethra stops potassium leaving the body, and rising potassium slows and then stops the heart. Cats have died overnight while their owners assumed they were constipated.

Most other urinary changes are not that, but they still matter. The commonest cause of a cat straining, going in and out of the tray and passing small amounts of bloody urine is feline idiopathic cystitis, a painful sterile inflammation of the bladder that is driven far more by stress and environment than by infection. Antibiotics do not fix it and are often given anyway.

• A male cat straining without producing urine is an emergency now, not in the morning.
• Straining looks identical whether the cat is trying to pass urine or faeces. Check the tray for what actually came out.
• Blood in a small volume of urine points at the bladder or urethra; a normal-sized wee that is discoloured points elsewhere.
• Drinking more and producing bigger clumps is a different problem entirely and usually points at kidney, thyroid or sugar disease.
• Urinating outside the tray is a medical sign before it is a behaviour problem.

Cat being petted on a blanket

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A cat that cannot pass urine dies within a day or two, and often faster.

When the urethra blocks, urine cannot leave, pressure backs up into the kidneys and the blood potassium climbs because potassium is normally excreted in urine. High potassium disturbs the heart's electrical conduction, producing a slow, weak, irregular heartbeat and then cardiac arrest. Male cats block far more often than females because the urethra narrows as it passes down the penis. If your male cat is repeatedly crouching, straining, crying, licking at his back end and producing nothing, go to a veterinary practice immediately, at any hour. Do not press on the abdomen to check; a distended bladder can rupture.
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Decide in 60 seconds

Why the male cat is the one that blocks

Urine leaves the bladder through the urethra. In a female cat that tube is short and relatively wide along its whole length. In a male cat it narrows as it passes through the pelvis and narrows further along the penis, and the neutered male penile urethra is narrower still than an entire male's.

Anything that forms a plug therefore lodges at the narrowest point. The plug is usually a mixture of crystalline mineral, protein-rich matrix from an inflamed bladder wall, red and white blood cells and cellular debris. Sometimes it is a true stone. Sometimes it is nothing solid at all, and the urethra is simply in spasm because it is inflamed and painful.

Once flow stops, three things happen in sequence. Pressure builds back through the ureters into the kidneys and shuts down filtration. Waste products that should be excreted accumulate in the blood. And potassium, normally removed in urine, rises steadily.

Potassium is the part that kills. Cardiac muscle depends on a steep potassium gradient across cell membranes to reset between beats. As blood potassium climbs, that gradient flattens, conduction slows, the heart rate falls and the rhythm becomes unstable. A cat that has been blocked long enough is often bradycardic and weak rather than agitated, which is exactly the point at which some owners decide the cat has calmed down.

That is the single most important thing to take from this article. A blocked cat that stops straining and goes quiet is usually worse, not better.

Feline idiopathic cystitis, the commonest cause and the least understood

In cats under about ten years old, most lower urinary signs are not infection and not stones. They are idiopathic cystitis: a painful inflammation of the bladder lining with no bacteria to find.

The bladder is normally protected by a layer of glycosaminoglycans that stops urine constituents contacting the wall. In affected cats that layer appears defective, so concentrated urine irritates the underlying tissue, nerves become sensitised, and the bladder becomes painful and urgent even when nearly empty.

What makes it distinctive is the link to stress. Affected cats show an exaggerated stress response, and episodes cluster around changes: a new cat in the house or visible outside, a new baby, building work, a house move, a change in routine, boarding, a full or dirty tray, or conflict at a shared resource. The bladder is the organ that expresses the stress, but the problem is a whole-cat one.

Episodes typically settle over several days whether or not antibiotics are given, which is exactly why antibiotics get the credit. The consequences of that are real: unnecessary antibiotic courses, missed environmental causes, and a cat that keeps relapsing.

The treatment that changes the pattern is environmental and dietary. Increasing water intake dilutes the urine and reduces irritation. Reducing stress reduces the frequency of episodes. Pain relief prescribed by a vet makes the episode itself shorter and less damaging.

What the litter tray tells you

Clumping litter is a diagnostic tool. Non-clumping litter hides volume, and pellet litters that fall through into a tray below hide it completely. If you are investigating a urinary problem, use a fine clumping litter for a week even if you normally use something else.

Cat with various pet items

Count the clumps and note their size.

You are building your own cat's baseline, not comparing against a formula. A cat that normally makes two or three clumps a day and is now making eight small ones has frequency. A cat that normally makes two and now makes two much larger ones has increased volume. Those point in completely different directions.

Frequency with small volume means the bladder or urethra: cystitis, crystals, stones, a partial obstruction.

Normal frequency with large volume means the cat is producing more urine: kidney disease, hyperthyroidism, diabetes, or occasionally a drug effect. That cat is usually also drinking more.

Look for blood.

Blood mixed evenly through a small clump points at the bladder. Fresh blood at the end of urination, or blood dripping without urination, points at the urethra. Some litters are sold with a colour indicator for blood, which can be useful, but a clean tray and a good look in daylight is usually enough.

Smell.

A sudden strong ammonia smell can mean infection, but it also occurs simply when a cat is producing very concentrated urine or when the tray has been left too long. It is a weak sign on its own.

Check for faeces separately.

This is the step that prevents the constipation mix-up. If the cat strains and a hard dry stool eventually appears, the problem is the colon. Cats with megacolon or chronic constipation strain, vocalise and posture exactly like cats with cystitis.

Differentials for a cat straining in the tray

Variation that changes the answer

Sex and neutering. Neutered males have the narrowest urethra and the highest obstruction risk. Females get cystitis and stones but very rarely block.

Age. Under ten, idiopathic cystitis dominates. Over ten, infection, kidney disease, hyperthyroidism and diabetes all become more likely, and a urinary change in an older cat should prompt bloodwork rather than just a bladder assessment.

Body condition. Overweight, inactive, indoor-only cats have a higher rate of lower urinary tract disease.

Diet. Cats on dry food alone produce more concentrated urine than cats eating wet food, because a cat does not fully compensate for dry food by drinking more.

Cat eating from a bowl

Household. Multi-cat homes generate the resource competition and social tension that drive idiopathic cystitis, and cats often hide that tension well. Trays, food and resting places should be duplicated and spread out, not lined up in one room.

Season and weather. Winter reduces activity and drinking in some cats, and cold outdoor conditions make outdoor cats hold urine longer.

Recent events. Cystitis episodes cluster after fireworks, building work, a new pet, a stay in a cattery, or the arrival of a stray cat in the garden.

What never to do

Do not wait until morning with a straining male cat.

Do not press or squeeze the abdomen to feel or empty the bladder. An over-distended bladder can rupture.

Do not give human painkillers. Paracetamol is lethal to cats even in tiny amounts, and ibuprofen causes kidney and gastric damage.

Do not start leftover antibiotics. Most young cats with these signs do not have an infection, and giving antibiotics before a urine sample is collected destroys the ability to culture it.

Do not add salt to the food to make the cat drink more.

Do not withhold water at night to reduce accidents.

Do not treat urinating outside the tray as naughtiness and punish it. Punishment increases stress and stress is the main driver of the commonest cause.

Do not switch a blocked or recently blocked cat straight onto a bargain dry food. Diet after an episode is a specific veterinary decision, and the wrong food is a genuine cause of relapse.

The routine that catches problems early

Scoop the tray at least once a day, every day, and look at what you are scooping before it goes in the bag. This is the whole monitoring programme.

Provide one more tray than you have cats, in different rooms, away from food, away from noisy appliances, and away from the route another cat has to guard.

Use an uncovered tray large enough for the cat to turn around in unless your cat clearly prefers otherwise. Many cats dislike hoods, liners and strong scents.

Move some or all of the diet to wet food if your vet agrees it suits your cat. This is the most effective way to increase total water intake.

Give water in wide shallow bowls away from the food, refreshed daily, and consider a second location. Some cats drink much more from moving water.

Weigh the cat monthly. Weight loss with increased drinking is a different set of diseases from bladder disease and needs blood and urine tests.

Reduce the friction points in a multi-cat house: separate feeding stations, multiple high resting places, and blocked sightlines to outdoor cats if that is the trigger.

Tabby cat with food bowl

When to get help

Go immediately, at any hour, for a male cat straining without producing urine, for any cat straining alongside vomiting, collapse or hiding, for a cat crying while in the tray, and for a cat that was straining and has now gone quiet and flat.

Book same-day for blood in the urine, for repeated small volumes, for a cat that will not settle, and for any cat that has stopped using the tray suddenly.

Book within a few days for gradually increasing thirst and urine volume, for weight loss with normal appetite, and for a cat over ten with any change in urinary habits.

Bring the tray record, a fresh urine sample if you have been able to collect one safely, the current and previous weights, the exact diet including brands and the proportion of wet to dry, the number of cats and trays in the home, and a list of anything that has changed in the household in the last month. Expect the vet to examine the abdomen, check the bladder size, run urine tests including concentration and sediment, and in an older cat run blood tests looking at kidney values, thyroid and glucose.